OFDMA (Orthogonal Frequency Division Multiplexing Access) is a nowadays widespread technology for data transmission which is based on the usage of a large number of closely-spaced orthogonal sub-carriers. In particular in wireless communication systems OFDMA becomes more and more popular and has been named as a candidate for future 4G standards.
As an example for the application of OFDMA in wireless communication systems it is to be referred to WiMAX. WiMAX is defined as World Wide Interoperability for Microwave Access based upon the standards family of IEEE 802.16. Just as the Wi-Fi Alliance certifies interoperable implementations of the IEEE 802.11 wireless LAN standard, the WiMAX Forum certifies interoperable implementations of IEEE 802.16 wireless standards.
In WiMAX, the frame filling process in the downlink direction is performed by a frame assembly scheduler that we refer as Downlink MAP (DL-MAP) scheduler. The job of a DL-MAP scheduler is to allocate downlink data packets, so called MPDUs (MAC Protocol Data Units), of a given size in bits into the downlink portion of a WiMAX frame. According to the two current WiMAX standards IEEE 802.16-2004 and 802.16e-2005, a WiMAX frame consists of a specific two dimensional area, wherein the two dimensions of the WiMAX frame are given in form of slots (time) and subchannels (frequency).
The task of the DL-MAP scheduler can be decomposed in two basic subtasks. First, it has to fit the previously mentioned MPDUs into rectangular shapes, defined as bursts in the WiMAX standards, where a specific MCS (Modulation and Coding Scheme) will be applied. By concatenating MPDUs belonging to different connection identifiers (CID) in a single burst the signaling overhead due to the DL-MAP size can be reduced. Second, it has to pack these bursts together within the rectangular WiMAX downlink frame minimizing the unused space that translates into a better exploitation of radio resources.
The two current WiMAX standards mentioned above do not provide any guidance about how a base station (and a DL-MAP scheduler, respectively) should realize the previously mentioned tasks. The performance of the system highly depends on the DL-MAP scheduler algorithm since it determines how efficiently the radio resources are used. The efficiency of the frame assembly scheduler is determined by the size of the empty space left at the end of the frame assembly as well as the amount of padding required to make the rectangles fit in the area of interest. Empty space and padding are wasted radio resources (i.e. bandwidth).
It is therefore an object of the present invention to improve and further develop a method and a communication system of the initially described type in such a way that the efficiency of radio resources usage in terms of empty spaces and padding in the OFDMA frame is enhanced and that the complexity required for the frame assembly scheduler is minimized.